1. Field
Embodiments described herein relate generally to an LED (Light Emitting Diode) Driver Circuit controlling an LED and an LED Driver system.
2. Background Art
Some conventional LED driver circuits include a constant current circuit for supplying a constant current to an LED connected to an external power supply, and a switch for controlling conduction and interception of the constant current to control lighting and extinguishment of the LED.
The constant current circuit is formed of, for example, an integrated circuit formed on a semiconductor substrate. It is supposed that the withstand voltage of this integrated circuit is, for example, 7 V and an operation voltage is 5 V. In this case, the operation voltage of the LED becomes approximately 3.5 V when the LED is lit (when a constant current of 20 mA is let flow).
In this case, the external power supply connected to the LED needs to output a power supply voltage of at least 8.5 V, which is the sum of the operation voltage 5 V of the integrated circuit and the operation voltage 3.5 V of the LED.
For example, when the constant current circuit is turned off, the current for driving the LED is lost and the voltage drop across the LED becomes 0 V. If the external power supply outputs a power supply voltage of 8.5 V, the voltage of 8.5 V is applied to the constant current circuit.
It is possible that the voltage applied to the constant voltage circuit will exceed the withstand voltage (7 V) of the LED driver circuit and, for example, dielectric breakdown of the constant current circuit will occur.